1. Field of the Invention
The invention relates, in general, to gas testing devices and, in particular, to a new and useful pump for gas test tubes. A similar bellows pump is known from German Pat. No. 10 07 523. Herein the gas to be tested is sucked through the gas test tube by means of a suction pump having the shape of a bellows pump, the gas escapes through the outlet valve on the side opposite the test tube when the bellows handle plates are pressed together, and it is sucked through the gas test tube when the handle plates are pressed back into their starting position by means of the force of a spring. This known bellows pump has the disadvantage that the volume of the sample is only consistent when the pump stroke is completed, it is not consistent, however, if the handle plates are e.g. not pressed together completely or are disposed at an angle due to carelessness. Furthermore, once the stroke is completed it is not possible to control whether an equalization of pressure has taken place and therefore whether the intended gas volume was sucked completely through the gas test tube before the next pump stroke can be executed.
German Pat. No. 33 30 578 shows an air feed pump whose device housing has the shape of a handle and the suction element is a bellows with a bottom plate. The bottom plate is connected to a centrally guided control rod, which is spring-biased in the direction of the suction stroke and can be arrested. The arresting takes place in the evacuated position of the bellows. Once the control rod is released, a complete suction stroke is executed. A window is provided in the device housing, in which a mark becomes visible with the end of the suction stroke. This air conveyor has a complicated design, however, and only allows for a limited pump stroke when operated with one hand. If the bellows is not pressed together completely, the control rod cannot be arrested and an undefined suction stroke can be executed, if, e.g., the air conveyor slips from the operator's hand while being operated with one hand. The mark in the window merely shows the final position of the bellows and does not allow for any control of whether the air is sucked through the gas test tube completely.
German Pat. No. 28 43 651 describes a function-testing device for a gas test device. It comprises a cylindrical housing with a colored jump-type membrane and a dispersion disc arranged correspondingly. The testing device is slipped onto the free end of the gas test tube, the sample air entering through a second opening at the cylindrical housing. For the determination of the pressure in the air flow, the open end is closed. The vacuum generating in the housing results in a movement of the jump-type membrane in the direction of the dispersion disc and therefore the color code becomes visible. A disadvantage of this device is that it has to be slipped onto the test tube as a separate component and that it requires special handling.